An impact copolymer (ICOP), e.g. propylene impact copolymer, is a heterophasic polymer characterized by a continuous phase that is a propylene-based polymer and a discontinuous elastomeric or “rubber” phase dispersed throughout the continuous phase. A conventional propylene impact copolymer production process is conducted in a two stage process. A first polymer (the continuous phase) is produced in a first polymerization reactor. The product of this first stage is then moved from the first reactor to a second reactor (i.e., impact reactor) where a second polymer (the discontinuous phase) is produced. The discontinuous phase is incorporated within a matrix of the continuous phase, thereby forming the impact copolymer. The resulting material is known as an impact copolymer, and it has beneficial properties, such as good impact resistance while maintaining much of its stiffness modulus. The weight fraction of the rubber material in the final ICOP product is called the fraction copolymer or rubber content, abbreviated Fc.
The discontinuous phase is typically elastomeric or rubbery in nature. This poses many processing difficulties. Due to the tackiness and stickiness of the second polymer, the flowability of the impact copolymer decreases as the amount of elastomer (the discontinuous phase) present in the impact copolymer increases. Decreased flowability is problematic, especially when producing high impact copolymer products (HICOP), e.g., with Fc greater than or equal to 30 weight percent (wt %). For example, particle stickiness and poor flowability of propylene impact copolymer with Fc greater than 30% may cause a number of production problems including but not limited to build up on the impact reactor walls, powder agglomeration, formation of large chunks, and/or hold-ups in the product purge bin resulting in reduced plant throughput or even plant shutdown.
Desirable would be a process for producing an impact copolymer whereby flowability of the polymer particles is maintained or improved as the Fc of the impact copolymer increases—particularly when the Fc for the impact copolymer is greater than 30%.